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99 lines
2.8 KiB
Markdown
99 lines
2.8 KiB
Markdown
---
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id: 587d7fac367417b2b2512bdc
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title: Use the d3.max and d3.min Functions to Find Minimum and Maximum Values in a Dataset
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challengeType: 6
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forumTopicId: 301496
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---
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## Description
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<section id='description'>
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The D3 methods <code>domain()</code> and <code>range()</code> set that information for your scale based on the data. There are a couple methods to make that easier.
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Often when you set the domain, you'll want to use the minimum and maximum values within the data set. Trying to find these values manually, especially in a large data set, may cause errors.
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D3 has two methods - <code>min()</code> and <code>max()</code> to return this information. Here's an example:
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```js
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const exampleData = [34, 234, 73, 90, 6, 52];
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d3.min(exampleData) // Returns 6
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d3.max(exampleData) // Returns 234
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```
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A dataset may have nested arrays, like the [x, y] coordinate pairs that were in the scatter plot example. In that case, you need to tell D3 how to calculate the maximum and minimum.
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Fortunately, both the <code>min()</code> and <code>max()</code> methods take a callback function.
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In this example, the callback function's argument <code>d</code> is for the current inner array. The callback needs to return the element from the inner array (the x or y value) over which you want to compute the maximum or minimum. Here's an example for how to find the min and max values with an array of arrays:
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```js
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const locationData = [[1, 7],[6, 3],[8, 3]];
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// Returns the smallest number out of the first elements
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const minX = d3.min(locationData, (d) => d[0]);
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// minX compared 1, 6, and 8 and is set to 1
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```
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</section>
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## Instructions
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<section id='instructions'>
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The <code>positionData</code> array holds sub arrays of x, y, and z coordinates. Use a D3 method to find the maximum value of the z coordinate (the third value) from the arrays and save it in the <code>output</code> variable.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: The text in the <code>h2</code> should be 8.
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testString: assert(output == 8 && $('h2').text() == '8');
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- text: Your code should use the <code>max()</code> method.
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testString: assert(code.match(/\.max/g), 'Your code should use the <code>max()</code> method.')
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='html-seed'>
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```html
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<body>
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<script>
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const positionData = [[1, 7, -4],[6, 3, 8],[2, 9, 3]]
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// Add your code below this line
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const output = undefined; // Change this line
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// Add your code above this line
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d3.select("body")
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.append("h2")
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.text(output)
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</script>
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</body>
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```html
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<body>
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<script>
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const positionData = [[1, 7, -4],[6, 3, 8],[2, 9, 3]]
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const output = d3.max(positionData, (d) => d[2])
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d3.select("body")
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.append("h2")
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.text(output)
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</script>
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</body>
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```
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</section>
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